[SY-I8] Grain Boundary Sliding: the best supporting role in ductile localization
Viscoplastic deformation of polycrystalline materials conditions many aspects of our everyday life from industrial hot forming of metallic items and durability of engineered structures, to glacier flow or plate tectonics powered by convection of Earth’s mantle rocks. Usually, polycrystalline viscoplastic deformation is largely based on crystal slip plasticity (CSP). However, grain boundary sliding (GBS) may become a dominant mechanism at high temperatures, small grain sizes and low strain rates. Both mechanisms are often considered to act in parallel and to contribute independently to the global behaviour. We considered different classes of polycrystalline materials, such as Silicates, NaCl and Aluminium, combining high temperature rheological investigations and micromechanical testing with in situ SEM multi-scale observations. In the latter case, we performed full field strain measurements, based on digital image correlation (DIC). For NaCl we could perform micromechanical tests in situ synchrotron X-ray microtomography and obtain both 2D and 3D strain fields. We show that for all of the considered materials CSP and GBS are not independent, but co-operative. Depending on microstructure and loading conditions, each one may be either the dominant strain cumulative mechanism, or a secondary mechanism, allowing for accommodation of the local strain incompatibilities related to the previous one. Both are necessary to ensure macroscopically homogeneous flow. We show examples of minor but crucial contribution of GBS to ductile localization phenomena and strain propagation throughout the microstructure.